1. Field of the Invention
This invention is related to integrated circuits formed on a semiconductor substrate. More particularly, this invention is related to integrated circuits having multiple selectable functions. These functions are selectable during operation by “software” programming.
2. Description of the Related Art
The structures of a field programmable gate array (FPGA) and programmed logic devices (PLD) are well known in the art. An FPGA and PLD each have configurable logic blocks (CLB) that will perform a Boolean logic operation on a group of input signals to perform a single complex logical function. The configurable logic blocks are then interconnected to form even more complex logic structures. The interconnection between the configurable logic blocks may be created by physically destroying fuses to break undesired connections or by activating pass transistors between wiring segments routed on the semiconductor substrate.
U.S. Pat. No. 5,740,069 (Agrawal et al.) describes a programmable integrated circuit that includes configurable logic blocks (CLB's), configurable input/output blocks (IOB's) and an interconnect network for providing program-defined routing of signals between the CLB's and IOB's. The interconnect network includes direct connect means for providing programmably-selectable, dedicated connections between a first CLB and one or more adjacent CLB's and further between a first CLB and one or more CLB's. The interconnect network also includes peripheral direct connect means for providing programmably selectable, dedicated connections between a first configurable IOB and first and second CLB's.
U.S. patent application Ser. No. 09/246,303, filed Feb. 8, 1999, teaches an integrated circuit module that has a common function known good integrated circuit die with selectable functions. The selectable functions are selected during assembly of the known good integrated circuit die. The known good integrated circuit die is mounted to a second level substrate. The second level substrate has wiring connections to the input/output pads of the known good integrated circuit die that select desired input functions and output functions.
Further, the wiring connections on the second level substrate provide signal paths to transfer signals to the desired input function and signals from the desired output function, and signals to and from the common functions. In addition, the wiring connections form connections between the input/output pads and external circuitry. To select the desired input functions and the desired output functions, appropriate logic states are applied to input/output pads connected to a function selector to configure a functional operation of the integrated circuit module. The second level module substrate has connector pins to provide physical and electrical connections between the external circuitry and the wiring connections on the second level substrate.
U.S. Pat. No. 5,360,992 (Lowery et al.) illustrates a semiconductor package which allows pinouts and bond options to be customized after encasement of a semiconductor die. The semiconductor package has two assemblies in a first embodiment and an optional third assembly in a second embodiment.
As semiconductor processing technology has improved, the number of electronic components has increased until it is now possible to incorporate multiple complete functions on an integrated circuit die. The concept of being able to have multiple selectable functions incorporated on a single integrated circuit die is known in the art. U.S. Pat. No. 5,511,182 (Le et al.) teaches a pin configuration logic circuit. The pin configuration logic circuit has a pin function register which defines a selected pin function, such as chip enable, write enable, and output enable to be provided as a chip select signal. The logic circuit allows an arbitrary pipeline length by causing the chip select signal to obey only the timing of the active cycle. For a two-deep access pipeline the logic circuit marks whether a first or a second cycle owns the pin. The pin configuration logic circuit uses the timing associated with the selected pin function to provide the chip select signal during the first cycle if the attributes of the cycle, such as an access to a region programmed in the pin function register, are met. During the second cycle, the pin configuration logic circuit further obeys the timing associated with the selected pin function if the attributes of that cycle are also met.
Further, the concept of reconfigurable circuit functions has been explored in the art. “Towards the Realistic Virtual Hardware”, Shibata et al., Innovative Architecture for Future Generation High-Performance Processors and Systems, October 1997, pp.50-55 describes a virtual hardware system that executes dataflow algorithms. It is based on an MPLD (Multifunction Programming Logic Device), an extended FPGA (Field Programmable Gate Array) that implements multiple sets of functions as configurations of a single chip. An algorithm to be executed on the virtual hardware is written in the DFC dataflow language and then translated into a collection of FPGA configurations, each representing a page-sized sub graph of the dataflow graph. Although an emulation system and software environment for the virtual hardware has been developed it has tended to be an unrealistic system due to the difficulty of the MPLD implementation. However, with recent technologies of semiconductors, FPGA and DRAM can be implemented into a single LSI chip. By using the common buffer of the DRAM array as a configuration memory of an FPGA, replacement of configuration data can be done at almost the same speed as an MPU. Compared with the MPLD approach, a large amount of data can be stored in the integrated DRAM.
While Shibata, et al. describes a configurable digital logic system, mixed signal (analog and digital) applications can be designed for reconfiguration. “Reconfigurable Signal Processing ASIC Architecture For High Speed Data Communications”, Grayver, et al., Proceedings of the 1998 IEEE International Symposium on Circuits and Systems, June 1998, ISCAS '98, Vol.4, pp.389-392 illustrates a flexible and reconfigurable signal processing ASIC architecture. The proposed architecture can be used to realize any one of several functional blocks needed for the physical layer implementation of high speed data communication systems operating at symbol rates over 60 M samples/sec. In fact, multiple instances of a chip based on this architecture, each operating in a different mode, can be used to realize the entire physical layer of high-speed data communication systems. The architecture features the following modes (functions); real and complex FIR/IIR filtering, least mean square (LMS) based adaptive filtering, Discrete Fourier Transforms (DFT) and direct digital frequency synthesis (DDFS), at up to 60 M samples/sec. All of the modes are mapped onto a common, regular datapath with minimal configuration logic and routing. Multiple chips operating in the same mode can be cascaded to allow for larger blocks.